Optical time domain reflectometers (OTDRs) are used in the telecommunications industry for testing, troubleshooting, and characterizing fiber optic cables to measure fiber cabling properties such as breaks, connector loss, splice loss, fiber attenuation, attenuation coefficients, fiber length, and other parameters that affect the signal transmission quality through the cable.
In testing a fiber with an OTDR, optical pulses are launched into the fiber under test from a pulsed laser diode at a low duty cycle. During the time between the optical pulses transmitted, returned light from the fiber under test is reflected back in the form of backscatter and reflections associated with events, such as connectors, and is then converted to an electrical signal, and processed for display. The signal is displayed as an amplitude in decibels versus a length plot showing a gradually decreasing backscatter energy level with reflective events appearing as pulses on the backscatter.